Epilepsy is a disorder characterized by chronic, recurring seizures, resulting from uncontrolled discharges of electrical activity in the brain. A seizure typically manifests itself as sudden, involuntary, disruptive, and often destructive sensory, motor, and cognitive phenomena. Seizures are frequently associated with physical harm to the body (e.g., tongue biting, limb breakage, and burns), a complete loss of consciousness, and incontinence. A typical seizure, for example, might begin as spontaneous shaking of an arm or leg and progress over seconds or minutes to rhythmic movement of the entire body, loss of consciousness, and voiding of urine or stool.
There have been a number of proposals from groups around the world for predicting seizures and warning the patient of the impending seizure. Most of such proposals attempt to analyze the patient's electroencephalogram or electrocorticograms (referred to collectively as “EEGs”), to differentiate between a “pre-seizure condition” and a “between-seizures condition.”
In the past, scalp EEG electrodes have been employed to record electrical activity produced along a human's scalp by the firing of neurons within the brain, as have headband arrays and cap electrodes. Unfortunately, these devices suffer from a number of disadvantages, including that they cannot typically be used in a convenient manner for chronic monitoring due to functional and aesthetic limitations. Scalp electrodes, for example, are generally unsuitable for measuring through the dead skin layer, which is approximately 30 microns thick, and typically require an electrolyte gel to increase the measurement repeatability.
In addition, current procedures generally result in electrodes having to be applied daily within the hospital and the patient's head being wrapped with tape. Typically, this can only be done for a maximum of seven consecutive days due to the instability of the electrode-tissue interface. For example, after multiple days, the skin may become brittle and irritated from the presence of the electrodes. In addition, patients may be cosmetically limited with bandaged electrodes around their head while the electrodes are on. Other electrodes have been designed for the scalp or for the cortex of the brain by numerous people, but they are typically battery powered and wired systems that require a craniotomy.
Current procedures also suffer from inaccuracies associated with artifact signals originating from locations other than the patient's brain. For example, muscle movements within the patient's scalp or eyes (e.g., blinking) create artifacts that are detected by the EEG electrodes, making it difficult to distinguish true neurological signals from other types of signals (i.e., noise). The artifacts may lead to erroneous determinations of the neurological state and/or erroneous predictions of neurological events, such as seizures.
Needs exist, therefore, for an improved EEG system and methods of use thereof. In particular, needs exist for EEG systems and methods that provide continuous monitoring of neurological signals and accurate predictions of neurological events.